An antenna is usually connected to a transmitter or receiver by way of a feed line. Antennas for use at radio frequencies are effective over a limited frequency range. When operation is required over a wide frequency range it is common to use multiple antennas with each antenna being optimized for a specific narrow band of frequencies. The desired antenna is manually selected with a switch or other means that connects that antenna's feed line to the transmitter or receiver.
If the antenna is a so-called active antenna (i.e., includes an antenna (pre-) amplifier), then the antenna amplifiers can easily be supplied with power. Furthermore, an antenna diagnosis can be simply performed for each individual antenna. However, for each antenna in an antenna system, an individual feed line must be provided. This condition makes the system costly, space consuming and heavy and, therefore, less suitable for automotive applications.
Also common are systems in which multiple (active) antennas are connected to multiple receivers and/or transmitters via a single feed line. When using a single feed line, however, antenna diagnosis is difficult to realize, if it can be realized at all. Thus, there is a need to provide a multi-band, multi-antenna system that overcomes the above-mentioned drawbacks.